Clinical presentation

Effects of local anaesthetic poisoning are dose related and develop rapidly after exposure. They include:

• neurological effects
  • early effects—tinnitus, dizziness, perioral tingling, numbness
  • severe effects—miosis, tremor, confusion, seizures (which can immediately precede cardiotoxicity), coma
• cardiovascular effects
  • can develop rapidly following intravascular injection
  • early effects—tachycardia, hypertension
  • severe effects—bradycardia, hypotension, QRS widening, atrial and ventricular arrhythmias, cardiovascular collapse, cardiac arrest
• respiratory effects—respiratory depression, apnoea
• methaemoglobinaemia—following large prilocaine and benzocaine exposures, but occasionally occurs with articaine, lidocaine and tetracaine (amethocaine) exposures.

Effects of local anaesthetic toxicity are worse in the presence of metabolic and respiratory acidosis. Altered conscious state, respiratory depression and seizures, which all contribute to acidosis, can therefore exacerbate the risk of life-threatening complications.